Conventionally, digital image data input to an image display apparatus is in a form in which pixels of red (R), green (G), and blue (B) are arranged into a square or rectangular parallelepiped array. In color display of the image display apparatus, a display effect viewed by a person greatly differs depending on a method for arranging the RGB pixels. In computer display, to express a sharp image, color units each having a set of pixels of R, G, and B are arranged in a square or rectangular parallelepiped array. When high resolution is required, a delta array with which the highest resolution is obtained among all forms of arrays formed with pixels of same number is often used. In the delta array, pixels are shifted by a half pitch for every line.
Conventionally, a method for improving resolution in the delta array is proposed. In such a method, a display element constituted by plural pixels for which light can be controlled according to image data, and pixel shifting means for shifting positions of pixels by half a distance between two adjacent pixels both longitudinally and transversely in a diagonal direction of the display pixels are used. In a technique disclosed in, for example Japanese Patent Application Laid-Open No. H7-134275, a rotating plate is used for changing a direction of light refraction, as the pixel shifting means.
Furthermore, in a technique disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-322908, to-be-displayed green display pixels excellent in human visibility are provided at potions shifted by half a pixel longitudinally and transversely on display elements of red, blue, and green to obtain high resolution with a single projector.
In a technique disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-70365, pixels are shifted using an image shifter to improve resolution.
Most of the conventional methods to improve resolution are proposed on the premise that an image is viewed from a distance (visible distance) at which a pixel structure is not recognized. Such methods are applied to a movie, and a television that are supposed to be viewed away from an image keeping a sufficient distance. Therefore, color components that constitute the displayed pixels and an image roughness such as out-of-color registration is recognized less frequently. However, image display apparatuses having a large screen used in a meeting have been increasing. Such image display apparatuses are often used in a situation in which the pixel structure can be recognized by viewers because of its use in a meeting or the like. Therefore, the color components that constitute the pixels, deviations of the respective colors, and the like should be considered.
The technique disclosed in the Japanese Patent Application Laid-Open No. 7-134275 and the technique disclosed in the Japanese Patent Application Laid-Open No. 2003-322908 cause frequent occurrence of out-of-color registration, resulting in degradation of an image quality.
Meanwhile, to improve the resolution of the display image by shifting pixels, there have been proposed a method by shifting pixels in one of a horizontal direction and a vertical direction or in plural directions combining the horizontal direction and the vertical direction, and a method for displaying an image in a delta array by diagonally shifting pixels using one pixel shifting means and improving resolution closer to a twofold resolution transversely and longitudinally at low cost. However, the techniques for displaying the high resolution image by arranging pixels in the delta array or diagonally shifting the pixel positions have the following problems. With the technique disclosed in the Japanese Patent Application Laid-Open No. 2004-70365, the resolution is improved only by increasing the number of display pixels. Data obtained by extracting only converted pixel data on pixels displayed in the delta array from image data (converted image data) having pixel data (converted pixel data) in the square or rectangular parallelepiped array generated by an image processing such as resolution conversion is displayed as output pixel data. The other converted pixel data is not used for the output image. Due to this, the data that cannot be used for the output pixel data is generated in the converted pixel data arranged in the square or rectangular parallelepiped array. Accordingly, image data dropouts occur to the displayed image and the image quality is degraded.
For example, an input image is made equal in resolution to converted image data in a square or rectangular parallelepiped array on the display apparatus, pixels of the input image and those of the converted image are arranged as shown in FIG. 6 according to the conventional technique. However, output pixels used for a displayed image are only those represented by diagonally shaded circles shown in FIG. 6 whereas data on pixels represented by white circles are not used. Accordingly, image data dropouts occur.
The present invention has been achieved to solve the above problems, and it is an object of the present invention to provide an image processing apparatus, an image display apparatus, an image processing method, and a computer product capable of generating and displaying output image data without image data dropouts, and improving a quality and a resolution of a displayed image by using converted pixel data that has not been conventionally used to generate the output image data to be displayed from among converted pixel data in a square or rectangular parallelepiped array obtained through an image processing such as resolution conversion in an image display apparatus in which pixels are arranged in a delta array or an image display apparatus in which pixels are shifted in a diagonal direction.